Java identifiers

• In programming languages, identifiers are used for identification purpose. In Java an identifier can be a class name, method name, variable name or a label.
• Identifiers are the name given to variables, classes, methods etc. Consider the Below code;

int score;

Here, score is a variable (an identifier). You cannot use keywords as variable name. Its because keywords have predefined meaning. For example,

int float;

The above code is wrong. Its because float is a keyword and cannot be used as a variable name.

Example Of Java Identifiers

public class Test
{
  public static void main(String[] args)
  {
  int a = 20;
  }
}

In the above java code, we have 5 identifiers namely :

• Test: class name.
• main: method name.
• String : predefined class name.
• args : variable name.
• a :  variable name.

Rules for Naming an Identifier

There are certain rules for defining a valid java identifier. These rules must be followed, otherwise, we get a compile-time error. These rules are also valid for other languages like C, C++.

• An identifier cannot be a keyword.
• Identifiers are case-sensitive.
• It can have a sequence of letters and digits. However, it must begin with a letter, $ or _. The first letter of an identifier cannot be a digit.
• Its convention to start an identifier with a letter rather and $ or _.
• Whitespaces are not allowed.
• Similarly, you cannot use symbols such as @, #, and so on.

Here are some valid identifiers:

score
level
highestScore
number1
convertToString
MyVariable
MYVARIABLE
myvariable
x
i
x1
i1
_myvariable
$myvariable
sum_of_array
easyto123

Here are some invalid identifiers:

class
float
1number
highest Score
@pple
My Variable  // contains a space
123easyto   // Begins with a digit
a+c // plus sign is not an alphanumeric character
variable-2 // hyphen is not an alphanumeric character
sum_&_difference // ampersand is not an alphanumeric character